Issue 44

St. John's wort reduces the effect of prescribed drugs

The Medicines Control Agency has recently instructed
manufacturers of St. John?s wort to apply warnings to all their products. The
warning advises consumers who wish to take St. John?s wort, but are taking
prescribed medicines, to consult with their doctor or pharmacist before taking
the product. The new labelling requirements for St. John?s wort products
are in response to a number of preliminary and case studies published in The
Lancet, which suggest that the herb disrupts the function of certain prescribed
medicines.

The drugs in question are theophylline (a bronchodilator),
cyclosporin (an immune suppressant), warfarin, digoxin, ethinyloestradiol and
desogestrel (both contraceptive pills). It seems that St. John?s wort increases
levels of an enzyme that is involved in the breakdown of these drugs. Is the
MCA overreacting? Especially, when you consider that several common foods such
as broccoli, cabbage and Brussels sprouts also interact with these drugs. Similarly,
so do charcoal-grilled beef, red wine, grapefruit juice and cigarette smoke.

Do GPs advise patients of these food interactions when
prescribing these medicines? It is important that consumers of St. John?s
wort products are aware of the possible interactions with prescribed medicines.
However, this type of information cannot be included on the label of unlicensed
St. John?s wort products and obtaining such a license is extremely difficult
under the current licensing regulations.

This prevents companies from applying helpful consumer
guidelines to ensure the appropriate and safe use of their products.